Vibration motor

Abstract

A vibration motor includes a base portion arranged to extend perpendicularly to a central axis extending in a vertical direction; a shaft having a lower end fixed to the base portion, and arranged to project upward along the central axis; a circuit board arranged above the base portion; a single annular coil attached to the circuit board, and arranged to have the shaft arranged inside thereof; a bearing portion attached to the shaft to be rotatable with respect to the shaft above the coil; a rotor holder attached to the bearing portion; a magnet portion including a plurality of magnetic poles, and attached to the rotor holder; an eccentric weight attached to the rotor holder; a spacer attached to the shaft between the bearing portion and the coil, and including an upper surface arranged to be in contact with a lower surface of the bearing portion; and a cover portion arranged to cover, at least in part, upper and lateral sides of the rotor holder and the eccentric weight, and fixed to an upper end of the shaft and an outer edge portion of the base portion. The spacer includes a lower surface arranged opposite to an upper surface of the coil in the vertical direction.

What is claimed is: 
     
       1. A vibration motor comprising:
 a base portion that extends perpendicularly to a central axis extending in a vertical direction; 
 a shaft including a lower end fixed to the base portion, and projecting upward along the central axis; 
 a circuit board above the base portion; 
 a single annular coil attached to the circuit board, and including the shaft arranged inside thereof; 
 a bearing portion attached to the shaft to be rotatable with respect to the shaft above the coil; 
 a rotor holder attached to the bearing portion; 
 a magnet portion including a plurality of magnetic poles, and attached to the rotor holder; 
 an eccentric weight attached to the rotor holder; 
 a spacer attached to the shaft between the bearing portion and the coil, and including an upper surface in contact with a lower surface of the bearing portion; and 
 a cover portion that covers, at least in part, upper and lateral sides of the rotor holder and the eccentric weight, and fixed to an upper end of the shaft and an outer edge portion of the base portion; wherein 
 the spacer includes a lower surface opposite to an upper surface of the coil in the vertical direction; 
 the bearing portion includes a lower surface of opposite to the upper surface of the coil in the vertical direction; and 
 all of the bearing portion, the spacer, and the coil overlap one another when viewed in the vertical direction. 
 
     
     
       2. The vibration motor according to  claim 1 , wherein the lower surface of the spacer is in contact with the upper surface of the coil. 
     
     
       3. The vibration motor according to  claim 2 , wherein the spacer is radially inside of the magnet portion. 
     
     
       4. The vibration motor according to  claim 3 , wherein the spacer is attached to the shaft through press fitting. 
     
     
       5. The vibration motor according to  claim 4 , wherein the spacer is made of a resin, and is in a shape of a circular ring or in a shape of letter C. 
     
     
       6. The vibration motor according to  claim 5 , wherein a radially outer end portion of the coil is radially outward of an outer circumferential edge of the magnet portion. 
     
     
       7. The vibration motor according to  claim 6 , wherein
 the coil includes two long side portions that extend in a longitudinal direction of the coil and to have the shaft arranged therebetween; 
 a width of an interspace between the two long side portions gradually decreases with increasing distance from a longitudinal middle of the coil; and 
 an electronic component is attached onto the circuit board at a position adjacent to one of the long side portions of the coil and spaced apart from the longitudinal middle of the coil. 
 
     
     
       8. The vibration motor according to  claim 6 , wherein
 the coil includes two long side portions that extend in a longitudinal direction of the coil and to have the shaft arranged therebetween; 
 one of the two long side portions includes a recessed portion that is recessed toward another one of the two long side portions at one position along the longitudinal direction; and 
 an electronic component is attached onto the circuit board at the one position along the longitudinal direction at or adjacent to the one of the two long side portions. 
 
     
     
       9. The vibration motor according to  claim 1 , wherein
 the coil includes two long side portions that extend in a longitudinal direction of the coil and to have the shaft arranged therebetween; 
 a width of an interspace between the two long side portions is smaller on one side of a longitudinal middle of the coil than on another side of the longitudinal middle; and 
 on the one side of the longitudinal middle of the coil, an electronic component is attached onto the circuit board at a position adjacent to one of the long side portions of the coil. 
 
     
     
       10. The vibration motor according to  claim 9 , wherein an angle defined between a plane including the central axis and passing through the electronic component and a plane including the central axis and passing through a longitudinal end portion of the coil is 45 degrees. 
     
     
       11. The vibration motor according to  claim 9 , wherein a lead wire extending from the coil is connected to the circuit board on an opposite side of the coil with respect to the electronic component. 
     
     
       12. The vibration motor according to  claim 9 , wherein a number of magnetic poles of the magnet portion is a multiple of four. 
     
     
       13. The vibration motor according to  claim 9 , wherein the magnetic poles are arranged at equal angular intervals in a circumferential direction. 
     
     
       14. The vibration motor according to  claim 9 , wherein
 the base portion includes a base central through hole passing therethrough in the vertical direction; and 
 the lower end of the shaft is fixed in the base central through hole. 
 
     
     
       15. The vibration motor according to  claim 14 , wherein an upper surface of an entire portion of the base portion which lies between the shaft and an inner circumferential edge of the coil in a plan view is arranged at a same vertical level. 
     
     
       16. The vibration motor according to  claim 15 , wherein the base portion is made of a metal. 
     
     
       17. The vibration motor according to  claim 16 , wherein
 the base portion includes:
 a base magnetic portion made of a magnetic metal; and 
 a base nonmagnetic portion made of a nonmagnetic metal, fixed to an edge portion of the base magnetic portion, and extending from the edge portion of the base magnetic portion perpendicularly to the vertical direction; 
 
 the base magnetic portion includes a plurality of magnetic element portions arranged in a circumferential direction, and located at positions opposed to the magnet portion in the vertical direction; and 
 the base nonmagnetic portion includes a plurality of nonmagnetic element portions arranged to alternate with the magnetic element portions in the circumferential direction, and located at positions opposed to the magnet portion in the vertical direction. 
 
     
     
       18. The vibration motor according to  claim 17 , wherein
 the base magnetic portion further includes a magnetic outer circumferential portion arranged to surround an outer periphery of the base nonmagnetic portion; 
 each of the magnetic element portions projects radially inward from the magnetic outer circumferential portion; 
 the base nonmagnetic portion further includes a nonmagnetic central portion to which the lower end of the shaft is fixed; and 
 each of the nonmagnetic element portions projects radially outward from the nonmagnetic central portion. 
 
     
     
       19. The vibration motor according to  claim 18 , wherein a radially inner end portion of each of the magnetic element portions is arranged opposite to the magnet portion in the vertical direction. 
     
     
       20. The vibration motor according to  claim 19 , wherein a circumferential width of a portion of each magnetic element portion which is opposed to the magnet portion in the vertical direction is equal to or smaller than a circumferential width of each magnetic pole of the magnet portion at any radial position. 
     
     
       21. The vibration motor according to  claim 20 , wherein a circumferential width of each of the magnetic element portions decreases in a radially inward direction. 
     
     
       22. The vibration motor according to  claim 17 , wherein
 the base nonmagnetic portion further includes a nonmagnetic outer circumferential portion that surrounds an outer periphery of the base magnetic portion; 
 each of the nonmagnetic element portions projects radially inward from the nonmagnetic outer circumferential portion; 
 the base magnetic portion further includes a magnetic central portion to which the lower end of the shaft is fixed; and 
 each of the magnetic element portions projects radially outward from the magnetic central portion. 
 
     
     
       23. The vibration motor according to  claim 22 , wherein a circumferential width of each of the magnetic element portions decreases in a radially outward direction. 
     
     
       24. The vibration motor according to  claim 23 , wherein a number of magnetic element portions is equal to or smaller than a number of magnetic poles of the magnet portion. 
     
     
       25. The vibration motor according to  claim 24 , wherein
 the number of magnetic element portions is equal to the number of magnetic poles; 
 the magnetic poles are at equal angular intervals in the circumferential direction; and 
 the magnetic element portions are at equal angular intervals in the circumferential direction. 
 
     
     
       26. The vibration motor according to  claim 25 , wherein
 the number of magnetic poles of the magnet portion is four; and 
 the number of magnetic element portions is four. 
 
     
     
       27. The vibration motor according to  claim 26 , wherein
 the base portion further includes a base projecting portion that projects radially outward from the cover portion; and 
 an angle defined between a first plane and a second plane is equal to 90 degrees divided by the number of magnetic poles of the magnet portion, the first plane including the central axis and a circumferential middle of the base projecting portion, the second plane including the central axis and a circumferential middle of one of the magnetic element portions that is closest to the first plane in the circumferential direction.